The present invention generally relates to an automatic gain control circuit and, more specifically, to an automatic gain control circuit in which the automatic gain control function is performed entirely in the digital domain.
Generally, automatic gain control is a process by which an input is scaled to an appropriate level so that an output that is dependent on the input can be maintained at a corresponding relatively constant level. There are various existing schemes or techniques that can be used to provide automatic gain control. These schemes generally fall into one of three categories including, analog, all-digital, and hybrid (e.g., digital control with a numerically controlled amplifier).
In some communication systems, the total power of a multi-channel signal is stabilized before the signal is provided to a digital channelizer. The digital channelizer then processes the signal to generate a number of individual channelizer outputs. Depending on the number of active channels within the signal and the relative power of each individual channel, mutual difference in the power between individual channelizer outputs can be quite high, for example, 30 dB. As a result, the function of automatic gain control is typically implemented at each channelizer output individually and all-digital automatic gain control techniques are usually used to achieve this function.
All-digital automatic gain control techniques further fall into one of two main categories including, direct automatic gain control and feedback-based automatic gain control. Direct automatic gain control is based on actual measurements of either the power or the average magnitude of the signal. Making these measurements is often computationally expensive. Feedback-based automatic gain control provides direct adjustment of the gain based on the output. FIG. 1 is a simplified schematic block diagram illustrating a typical circuit providing feedback-based automatic gain control. Typically, feedback-based automatic gain control is more suitable for applications where minimum hardware complexity is desired. Existing all-digital automatic gain control techniques have their shortcomings and disadvantages. For example, currently, even the simplest implementation of a feedback-based automatic gain control requires multipliers on a signal path. If the dynamic range of input data is dozens of decibels, the gain value must be represented by a long wordlength, which essentially means increasing implementation complexity of a multiplier. Hence, it would be desirable to provide a method and system that is capable of achieving improved automatic gain control in a digital domain with reduced implementation complexity.